1. Field of the Invention:
This invention relates to an injection molding apparatus for providing a continuous length of slide fastener chain by repeating the steps of advancing intermittently a pair of stringer tapes through the spacing between a pair of molds of injection molding means, closing the molds on the tapes during the pauses in the advance of the tapes to injection-mold fastener elements along the opposing inner edges thereof, and subsequently opening the molds to permit the advance of the tapes in the form of a molded slide fastener chain.
2. Description of the Prior Art:
In the repetitive injection molding of fastener elements with the injection molding apparatus of the type described, it is known that the molded fastener elements will be attached to the stringer tapes askew and at an irregular pitch unless the stringer tapes are subjected to a constant tension and clamped by the pair of molds at a predetermined position at the time of each molding operation. It is also known that the molding requires that the pitch of the fastener element at the connecting portion between a previously molded fastener element row and a subsequently molded fastener element row be the same as the pitch between adjacent ones of the fastener elements which are molded in each fastener element row, or such that a predetermined spacing will be maintained between the previously molded and subsequently molded fastener element rows. To this end, it is conventional practice to apply a tensile force to the tapes by providing the molds with tensioning means, and further to control the feed of the fastener element-equipped tapes, namely the fastener chain, through the use of positioning means so as to maintain a predetermined spacing between fastener elements at the portions where a previously molded fastener element row adjoins a subsequently molded fastener element row. A basic method of carrying out such positioning, for example as disclosed in Japanese Patent Public Disclosure No. 134533/77, comprises clamping the molded fastener chain in a clamping device to feed constant lengths of the fastener chain by means of a feed cylinder, and retaining the posterior end of previously molded fastener chain in place by bringing a pressing plate into pressured contact with a guide plate provided on one of the molds. Another method as disclosed in Japanese Patent Publication No. 4771/63 comprises feedng previously molded fastener chain by an amount greater than that required to feed the fastener chain up to a fixed position, and then causing the fastener chain to return or move back by the amount of the extra feed to set the stringer tapes at the predetermined position. However, the actual method of moving back the stringer tapes makes use of a retaining body for a roller that supports the stringer tapes, as well as a pinion and rack adapted to shift the roller retaining body in the direction that causes the stringer tapes to move back. The apparatus for practicing this method therefore becomes extremely complicated, as does that of the former example which relies upon the clamping device.